This invention relates to a wrench assembly for use with mine support bolts such as are used in supporting the side walls of underground mine passages.
In underground operations, such as mining or excavating, it is common practice to reinforce side walls by bolts that are inserted into a drill hole of the rock formation and are secured thereto by either engagement of an expansion shell on the end of the bolt or adhesively bonding the bolt by a thermosetting resin placed in the drill hole so that upon curing the bolt is united with the rock formation. The drill hole is usually formed at an incline from the vertical plane of the side wall of the formation. The support bolts, which may be upwards of eight feet in length, are rotated in the drill holes by a mine bolting machine. A wrench which engages the head of a bolt is driven by the bolting machine. The typical wrench has an elongated shaft joined to a socket.
In a typical mine side wall support arrangement the support bolt has a tendency to shift its position within the drill hole. When a bolt shifts its longitudinal axis will no longer be in line with the axis of the drill hole. The wrench is always aligned with the drill hole and when a bolt shifts this wrench will not shift with it. As a result the socket of the wrench will often come off of the bolt head and the bolting machine will then cease tightening the bolt within the drill hole. The bolt will, in virtually all cases, remain loosely installed and will not provide the required support to the side wall. The loose bolt problem is without satisfactory remedy as the only way to tighten the shifted bolt is by hand, and that method will not provide the compression force needed to result in the desired support.
This invention overcomes the problem of shifting side wall support bolts by providing a wrench which will bend as the bolt shifts and thereby permit the bolting machine to continue to drive the bolt until the necessary compression force is placed on the side wall of the rock formation.